Fiber optics are used in a wide variety of applications. The use of optical fibers as a medium for transmission of digital data (including voice, internet and IP video data) is becoming increasingly more common due to the high reliability and large bandwidth available with optical transmission systems. Fundamental to these systems are optical subassemblies for transmitting and/or receiving optical signals.
Optical subassemblies typically comprise an interposer. As used herein, an interposer functions as a substrate for optical, opto-electrical, and electrical components and provides interconnections to optically and/or electrically interconnect the optical/opto-electrical/electrical components. For example, a typical interposer may comprise a substrate, for example, silicon, having one or more grooves formed therein for securing an optical fiber. The conventional groove is formed in the shape of a “V” by wet etching the substrate to include two sidewalls that retain the optical fiber along its length and an end face that is used as a mirror device. The conventional V-groove has a particular pitch α, which is the angle between the walls of the V-groove and a top or reference surface in which the V-groove was etched. Each of the sidewalls and the end face are typically formed at a precise angle of 54.7 degrees from the reference surface due to the crystalline structure of silicon.
During operation, the end face of a conventional interposer V-groove is metalized so that it may be used as a mirror to reflect light between the optical/opto-electrical component and the optical fiber. For example, in the case of a transmitter, an opto-electrical light source emits a cone-shaped light beam onto the V-groove end face mirror. The V-groove end face mirror reflects the light through an end of the optical fiber retained in the V-groove. As discussed above, the surface of the V-groove end face is at an angle of precisely 54.7 degrees from the reference surface. As such, light is reflected off the groove end face mirror through the optical fiber at approximately −9.3 degrees from the reference surface and also from the longitudinal axis of the optical fiber retained in the V-groove. Therefore, current devices utilizing the end face mirror of the groove to launch light through an end of the optical fiber cause much of the light to be reflected away from the axis of the optical fiber resulting in non-optimal signal transmission performance.
Therefore, Applicants recognize that there is a need for an improved optical coupling between the optical/opto-electrical component and the optical fiber or an optical planar waveguide. Additionally, Applicants recognize that this optical coupling should be achievable through passive alignment rather than active alignment to facilitate economic production of the subassembly. To this end, Applicants recently filed a new patent application (U.S. application Ser. No. 12/510,954, incorporated herein referenced) disclosing a multi-faceted fiber end face mirror for optical coupling. Specifically, the facets of the fiber end face mirror included a 54.7 degree facet to mechanically contact the end face of the V-groove to precisely position the optical fiber end face mirror in the V-groove along the longitudinal axis and under the emission aperture of the opto-electrical device. Additionally, another facet was a 45 degree facet to facilitate optimal optical coupling between the optical axis of the fiber and the optical axis of the opto-electrical device. Additional facets were also disclosed for enhancing performance. Each of these facets would then be coated with a metal to act as a reflective mirror surface.
Although this development improved the optical performance and facilitated passive alignment of the subassembly, it also required coating the fiber end face on a number of different facets with a metallic/reflective coating. Applicants have identified an additional need to avoid the requirement for depositing a reflecting coating on fiber end faces as such a process tends to be difficult and expensive and may be time prohibitive in a high volume application.
Therefore, a need exists for a simplified means for preparing an optical assembly having good optical coupling to either an optical fiber or an optical planar waveguide and performing this optical coupling by passive alignment. The present invention fulfills this need among others.